Basically, there are three known processes for the waterproofing of leather and skins, namely:
1. impregnation by incorporation of water-insoluble substances, for example solid fats, waxes or special polymers, PA1 2. impregnation by incorporation of water-swelling substances which form high-viscosity emulsions on taking up water and which block the interstices between the leather fibers, for example special emulsifiers of the w/o type, PA1 3. treatment with hydrophobicizing substances, for example aluminium, chromium and/or zirconium complexes, silicones or organic fluorine compounds. PA1 (a) semiesters of maleic acid with oleophilic alcohols and/or lower alkylene oxide adducts thereof and PA1 (b) acrylic acid and/or methacrylic acid as principal components which may additionally contain PA1 (c) small quantities of other hydrophilic and/or oleophilic comonomers in the oligomer molecule,